Summary: this change will allow the slider to have different thumb images .
Sets an image for the thumb. It only supports static images
Closes https://github.com/facebook/react-native/pull/3849
Reviewed By: svcscm
Differential Revision: D2665699
Pulled By: nicklockwood
fb-gh-sync-id: 3a767e43170074e2419067d5c8eae61668ebb5e9
Manuel Nakamurakare